# Linear Regulator Fundamentals - PowerPoint PPT Presentation

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Linear Regulator Fundamentals. 2.2 NPN. Linear-Regulator Operation. Voltage feedback samples the output R1 and R2 may be internal or external Feedback controls pass transistor’s current to the load. V. V. IN. OUT. PASS TRANSISTOR. R1. ERROR. C. AMP. C. IN. R. OUT. LOAD. R2. V.

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Linear Regulator Fundamentals

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## Linear Regulator Fundamentals

2.2 NPN

### Linear-Regulator Operation

• Voltage feedback samples the outputR1 and R2 may be internal or external

• Feedback controls pass transistor’s current to the load

V

V

IN

OUT

PASS

TRANSISTOR

R1

ERROR

C

AMP

C

IN

R

OUT

R2

V

REF

### NPN "Quasi-LDO" Voltage Regulator

• The NPN-Quasi-LDO has the following Characteristics:

• Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage

• Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators

• Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO

### Losses in the NPN "Quasi-LDO"

Simple Model of Losses in the NPN "Quasi-LDO"

### Driving the NPN "Quasi-LDO" Pass Element

The drive current for a load current requirement of 5mA

### Drive Current vs. Low/High Load Current

Increasing the load current requirement to 500mA

### Summary

• The NPN-Quasi-LDO has the following Characteristics:

• Requires the input voltage to be at least 0.9V to 1.5V higher than the output voltage

• Has higher Ground pin current than the NPN-Darlington, but less than the PNP-LDO Voltage Regulators

• Requires an output capacitor, but, generally, has no specific ESR requirement like the PNP-LDO